I would frankenstein together a new pattern using this neckline/upper bodice:

with the waist-down portions of any wedding dress pattern of this type:

For fabrics, I'd probably look at lycra/spandex for the yellow and green (homage to the superhero go-to) although it really looks like latex, which I have no experience working with. The beige almost seems to sparkle like sequins but it might be best to go with the same shine-level as the green & yellow fabrics. The shoulders have to be stuffed like crazy and the pattern will need to be altered to create that shape. I'd look into leg-of-mutton sleeves from the 1900's to see how large and weird they can get.

And of course, a floor-length, very soft, full, and beautiful petticoat underneath that you can let peek-a-boo.

I think it would look really awesome made out of a liquid-look spandex or vinyl or otherwise - a fabric that's like her actual clothing in canon was the vibe I was getting. Harder to work with, but an idea I just wanted to throw out.

I'm not sure if it would "read" as well as being her if it was made out of regular pretty dress material, but it's up to you.

When making something, break it down into smaller questions. "What will it be made out of ?", "How will I support this shape ?"